Agriculture Reference
In-Depth Information
the soil bacterium
Bacillus thuringiensis
(Bt)
that make the plant resistant to certain
lepidopteran and coleopteran pest species.
h e most widely used examples are Bt maize
and Bt cotton. In 2012, Bt maize was grown
on 47 Mha (see Fig. 1.2) in more than 15
dif erent countries. h e biggest Bt maize
areas are found in the USA, Argentina, South
Africa, Canada and the Philippines. Bt
cotton was grown on 23 Mha in 2012, mostly
in India, China, Pakistan and the USA, but
also in a number of other countries (James,
2012).
In cotton, high amounts of chemical
insecticides are normally used to control the
bollworm complex, which is the main Bt
target pest. Accordingly, Bt cotton adoption
allows signii cant insecticide reductions,
ranging from 20% to 80% on average. Yield
ef ects are also signii cant, especially in
developing countries. In some countries,
such as Argentina, conventional cotton
farmers underuse chemical insecticides, so
that insect pests are not controlled ef ec-
tively (Qaim and Janvry, 2005). In India,
China and Pakistan, chemical input use is
much higher, but the insecticides are not
always very ef ective, due to low quality,
resistance in pest populations and incorrect
timing of sprays (Huang
et al
., 2003; Qaim
et
al
., 2006).
For Bt maize, similar ef ects can be
observed, albeit generally at a lower magni-
tude. Except for Spain, where the percentage
reduction in insecticide use is large, the
more important result of Bt maize is an
increase in ef ective yields. In tropical and
subtropical areas, mean yield ef ects are
higher, because there is more pest pressure.
h e average Bt maize yield gain of 11% in
South Africa refers to large commercial
farms. h ese farms have been growing
yellow Bt maize hybrids for several years.
Gouse
et al
. (2006) also analysed on-farm
trials that were carried out with smallholder
If insect pests are controlled ef ectively
through chemical pesticides, the main ef ect
of switching to Bt crops will be a reduction in
insecticide applications. However, there are
also situations where insect pests are not
controlled ef ectively by chemical means,
due to the unavailability of suitable
insecticides or other technical, i nancial or
institutional constraints. In those situations,
Bt adoption can help reduce crop damage
and thus increase ef ective yields (Qaim and
Zilberman, 2003). Table 14.2 coni rms that
both insecticide-reducing and yield-
increasing ef ects of Bt crops can be observed
internationally.
Table 14.2.
Average effects of Bt cotton and Bt maize. (From Qaim, 2009; Kouser and Qaim,
2013.)
Insecticide reduction
(%)
Increase in yield
(%)
Increase in profi t
(US$/ha)
Country
Bt cotton
Argentina
47
33
23
Australia
48
0
66
China
65
24
470
India
41
37
135
Mexico
77
9
295
Pakistan
21
28
504
South Africa
33
22
91
USA
36
10
58
Bt maize
Argentina
0
9
20
Philippines
5
34
53
South Africa
10
11
42
Spain
63
6
70
USA
8
5
12
